In an operating room, for any surgery requiring general anesthesia, the patient is given an intravenous or intramuscular dose of potent paralytic drugs (Neuro-muscular blocking agents (NMBA) (e.g. Vecuronium). These drugs are given after the induction of anesthesia (before surgery begins), and re-dosed during long duration surgeries, to ensure that a state of paralysis is maintained throughout the entire surgical course. At the end of surgery, the anesthesia provider has to make a judgment regarding the degree of paralysis of the patient so that a correct dose of antidote, or NMB Reversing Agent (NMBRA) (e.g. Neostigmine), can be administered to reverse the paralysis. Upon receiving the correct dose of NMBRA, the patient regains consciousness and is brought back to a state of wakefulness.
The success of administering and reversing general anesthesia depends heavily on using the correct dose of NMBA and NMBRA. More specifically, an excessive dose as well as a low dose of antidote can be dangerous and life threatening. Administering excessive NMB antidote runs the risk of recurarization in some patients. Recurarization is subjective to a patient and his condition; it is not predictable, nor easily reproducible. Failure to recognize and promptly treat recurarization often leads to death.
Currently, there are some electro-medical devices under various names such as Peripheral Nerve Stimulator (U.S. Pat. Nos. 4,157,087, 5,131,401) etc., that provide a modicum of monitoring of patients under anesthesia using NMBA. However, clinical criteria are subjective, causing doubt about clinical residual NMB.
A problem with current patient monitoring systems is the lack of a quantitative measure of the degree of patient neuro-muscular blockade (paralysis). Most anesthesiologists today use a method of directing a train of electrical pulses toward a patient nerve in select area (e.g., the thumb) and observing patient response (e.g., twitching of the thumb). The patient response varies from individual to individual significantly. Yet, there is no device that helps the anesthesiologist accurately determine the end point of the paralysis. Determining the dose of NMBRA to use remains an “art” based on the anesthesia provider's memory, experience, and judgment.
The current devices emit four electrical pulses (also known in the industry as “Train Of Four” (TOF)) that are directed towards a nerve on the surface of the skin, which further supply electrical impulses to a muscle group. A patient's muscle has a unique neuromuscular threshold to electrical stimulation that is further modulated by electrode placement and quality of electrode's electrical contact with the skin, and currently available devices are unable to factor in these neuromuscular thresholds. Some devices do not keep a record of the electrical pulses administered and/or the corresponding patient's response to the stimulus to an electrical ‘train of four’. The practice depends on the anesthesiologist's training and experience. Therefore, there is little to no quantitative measure of the extent of neuro-muscular blockade and the gradual wearing out of the efficacy of the paralytic drugs administered with the current generation of diagnostic devices that are commercially available.
The current diagnostic devices that try to instrument and measure the twitch due to TOF are subjective and based on the assessment of the anesthesia doctor. Furthermore, they do not provide robust quantification of degree of paralysis to aid determination of the dosage of NMB-reversal agent (NMBRA) that should be administered to quickly and safely bring back the patient to recovery, a natural phase of breathing, and wakefulness. This quite often is one of the causes of death after anesthesia and surgery. The Journal of Anesthesia and Analgesia, July 2010 commented upon this lamentable state of affairs in a series of articles among other medical literature in anesthesia.
At least based on the above, there is a need for a device that can accurately measure NMB and give reliable information to determine patient's level of paralysis, guiding the anesthesiologist's determination of correct NMBRA dosage. Such a device would aid patient recovery during and after the end of clinical anesthesia in the operating room, and reduce the chances of partial reversal due to inaccurate assessment and consequent over-dosing, which often results in deaths at post operative care unit or intensive care unit.